Formation of Cyclopentenethiones via Cyclization of β-Thioallyl Cations

Article abstract of DOI:10.1021/jo00280a038

Reaction of 2,2-diaryl-3-<2',2'-dimethyl-1'-(trimethylsilyl)-3'-butenylidene>thiiranes 1a and 1b with BF3*Et2O resulted in facile formation of stable cyclopentenethiones 3a and 3b, by a new type of cyclization via the initially generated thioallyl cations.The mechanism of this Lewis acid promoted isomerization of allene episulfides 1a and 1b is rationalized by taking into account the conformation of the thioallyl cation and the effect of the aromatic substituents.The structure of 3a, a novel example of a crystalline aliphatic conjugated thione, has been determined by X-ray crystallographic analysis.